Fluoropolymers, i.e. polymers having a fluorinated backbone, have been long known and have been used in a variety of applications because of their desirable properties such as heat resistance, chemical resistance, weatherability, UV-stability etc. Various fluoropolymers and they applications are, for example, described in “Modern Fluoropolymers”, edited by John Scheirs, Wiley Science 1997, “Fluoropolymer Applications in Chemical Processing Industries, edited by Sina Ebnesajjad and Pradip Khaladkar, William Andrew Inc, Norwich, N.J., USA, 2005.
Typical fluoropolymers include homo or copolymers of a gaseous fluorinated olefins such as tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE), vinylidene fluoride (VDF) and/or hexafluoropropylene (HFP) or comonomers of one or more of the afore-mentioned monomers with one or more comonomers, such as, for example, perfluorovinyl ethers (PVE), perfluoroallyl ethers, perfluoro alkoxyvinyl ethers, perfluoro alkoxy allyl ethers or non-fluorinated olefins such as ethylene (E) and propylene (P). Typically, the content of these comonomers in the polymer is less than 50 mol %, less than 30 mol % or less than mol 10%, such that the overall characteristic of the polymer remain that of a fluoropolymer and are not those of a non-fluorinated polymer.
To modify or improve the properties of fluoropolymers, in particular to introduce or improve elastic properties, functional groups are typically introduced into the polymer, for example functional groups capable of cross-linking (or curing) the fluoropolymers. In particular fluoroelastomers, i.e. fluoropolymers having elastic properties, are prepared by copolymerizing so-called cure site monomers, which are monomers bearing functional groups which allow for cross-linking of the resulting fluoropolymers. Typical cure-site monomers are olefins or vinyl ethers containing one or more chlorine, bromine, iodine atoms or nitrile groups. Examples of such cure-site monomers and elastomers containing them are described, for example, WO 01/27194, EP-A1-1 211 265 or EP 0 868 447. In U.S. Pat. No. 6,417,379 a process is described wherein sulfonyl azide groups are introduced as functional groups into the polymer backbone.
There is still a desire to find further methods of introducing functional groups into a fluoropolymer and for fluoropolymers containing alternative functional groups. Desirably such process allows for the preparation of fluoroelastomers.